A radio frequency power amplifier (RF power amplifier) is a type of electronic amplifier that converts a low-power radio-frequency signal into a higher power signal. There are many classes of power amplifiers which are used to distinguish the electrical characteristics and methods of operation of the power amplifiers. Accordingly, the classes of power amplifiers are mainly lumped into two basic groups. The first are the classically controlled conduction angle amplifiers forming the more common amplifier classes of A, B, AB and C, which are defined by the length of their conduction state over some portion of the output waveform, such that the output stage transistor operation lies somewhere between being “fully-ON” and “fully-OFF”.
The second set of amplifiers are the newer so-called “switching” amplifier classes of D, E, F, G, S, T among others, which use digital circuits and pulse width modulation (PWM) to constantly switch the signal between “fully-ON” and “fully-OFF” driving the output hard into the transistors saturation and cut-off regions.
Different types of power amplifier architectures may include different types of components. For example, the type S power amplifiers convert analogue input signals into digital square wave pulses by a delta sigma modulator, and amplifies them to increases the output power before finally being filtered by a band pass filter.
In particular, delta sigma modulation is a method for encoding analog signals into digital signals as found in an analog to digital (ADC) converter. Delta sigma modulation may also be used to transfer high bit-count low frequency digital signals into lower bit-count higher frequency digital signals as found in digital to analog (DAC) operation. This technique is popular in modern electronic components such as converters, frequency synthesizers, switched-mode power supplies and motor controllers, due to its cost efficiency and reduced circuit complexity.
In addition, delta sigma modulators may reduce noise using noise shaping and increase signal resolution using filtering. In noise shaping, noise is filtered by a noise shaping filter. This means that the noise is reduced inside frequencies of interest and increased outside the frequencies of interest. As a result, the resolution of the signal is increased. In delta sigma modulators, noise shape filtering may be performed at an over-sampled rate. The noise shaping is achieved by subtracting estimated in-band noise from an input signal of the delta sigma modulator. The estimated in-band noise subtraction is done through the feed-back path in the modulator. A post noise shaping filter can be placed after the modulator that cuts the noise from outside the frequency of interest which, in turn increases the signal's resolution.
As such, delta sigma modulators can provide a less complex and cost efficient manner to perform Analog to Digital (A/D) and Digital to Analog (D/A) conversion in many electronic components including, but not limited to ADCs, DACs, frequency synthesizers, switch-mode power supplies, and motor controllers.